1. Field of the Invention
The present invention relates to an infection control apparatus for an implantable heart stimulator of the type having a pulse generator for delivering electric stimulation pulses to a patient's heart through a lead connectable to the pulse generator the pulse generator housing being electrically conductive.
2. Description of the Prior Art
Implantable heart stimulator pocket infection is a severe complication which often ends up in explanation of the stimulator. The reason therefor is that conventional treatment with antibiotics cannot eradicate the infection. This seems to depend on the circumstance that the bacteria live in a biofilm formed around the exterior surfaces of the implanted stimulator, which film blocks antibiotics. The bacteria may also live passively on a very low metabolism and can therefore not be treated successfully by antibiotics.
A method of enhancing the effect of antibiotics by applying an electrical field across the biofilm is described in U.S. Pat. No. 5,312,813. This method is based on findings by J. W. Costerton et.al. Their studies have shown that the infection can be completely cured and no explanation has to take place by applying an electric field or a small current across the biofilm during antibiotic treatment, cf. also ASAIO Journal 1992, p.M-174 M178, Khoury et.al, “Prevention and Control of Bacterial Infections Associated with Medical Devices”, and Antimicrobial Agents and Chemotherapy, Vol. 38, No. 12, December 1994, p. 2803-2809, Costerton et.al., “Mechanism of Electrical Enhancement of Efficacy of Antibiotics in Killing Biofilm Bacteria” In these studies, generally, a low electric current of the order of 15-400 μA/cm2 is applied onto the infected surface while immersed in a buffer with antibiotics. In the most successful studies a total killing of microorganisms was reported after only 8 hours of current and antibiotic treatment—tobramycin 2.5 mg/l, 15-400 μA/cm2 during 8 h. This effect has been termed “the bioelectric effect”.
These studies suggest that the electric field needs to be applied in close proximity to the infected implant. A passive electric field will not be effective, but a current should be conducted between electrodes in the biofluid surrounding the implanted device. A possible explanation to the observed effect is that electrochemically generated products are needed for the bioelectric effect to occur. At the titanium surface, titanium being normally used in heart stimulator housings, the following electrochemical processes take place.
At the anode:
1) 2H2O→O2+4H++4e−
2) 2Cl−→Cl2+2e−
3) Ti+2H2O→TiO2+4H++4e−
At the cathode:
1) O2+2H2O+4e−→4OH−
2) 2H2O+2e−→H2+2OH−
It is supposed that primarily the produced oxygen and chloride gases have an influence on the biofilm attached to the surface. It is also supposed that the fact that the pH-value is towered at the anode and increased at the cathode is significant for the influence and viability of the biofilm.
An infection that is initiated in the stimulator pocket will also often start to spread along the lead. The polymer surface of the lead may be a substrate for the bacteria and makes it easy for the bacteria to attach. At the time when a pocket infection is clinically manifested, in many cases the infection has already spread some distance from the stimulator pocket along the lead.